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Difference between revisions of "x86/adx"
(→Overview: Changed "an register" to "a register"; changed "effecting flags" to "affecting flags.") |
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− | * To add a constant to | + | * To add a constant to a register without affecting flags, you can use the <code>LEA reg, [reg + n]</code> instruction |
<source lang=asm> | <source lang=asm> |
Latest revision as of 11:28, 10 August 2021
x86
Instruction Set Architecture
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ADX is an x86 instruction set extension that introduced arbitrary-precision arithmetic operations.
Overview[edit]
ADX introduced two new instructions:
- ADCX
- ADOX
They are similar to the ADC instruction by doing a add with overflow, but
- ADCX uses the Carry flag as source and destination of overflow and leaves the other flags untouched
- ADOX uses the Overflow flag as source and destination of overflow and leaves the other flags untouched
This allows two parallel addition of multi-precision numbers because both have their separate carry flag.
Note:
- To add a constant to a register without affecting flags, you can use the
LEA reg, [reg + n]
instruction
xor rax, rax
lbl:
mov rbx, [r8 + r15]
adcx rbx, [r9 + r15]
mov [r9 + r15], rbx
mov rbx, [r10 + r15]
adox rbx, [r11 + r15]
mov [r11 + r15], rbx
lea r15, [r15 + 8]
dec r14
jnz lbl